The torque converter comprises a pump impeller, a turbine runner and a stator supported in a one-way clutch. The pump impeller is connected to the output shaft of an engine through a front cover concentrically fixed to the pump impeller, while the turbine runner is connected to the input shaft of a transmission gear.
In an automatic transmission for a motor vehicle, a direct-coupling clutch is included in the torque converter for directly connecting the output shaft of the engine and the input shaft of the transmission gear. For this purpose, a clutch disk is mounted axially slidably on the input shaft of the transmission gear and is adapted to be rotatable together with the turbine runner in the space formed between the front cover and the turbine runner, while a flat surface is formed on the front cover for affixing a frictional material or for frictionally engaging with a frictional material. The output shaft of the engine and the input shaft of the transmission gear are directly connected by the frictional engagement of the clutch disk and the front cover through the frictional material.
It is desirable to provide either the front cover or the clutch disk with a frictional material of an increased diameter and of a flat surface and to make the entire area of the frictional material to be in contact with the counterpart when the direct-coupling clutch is engaged in order to provide an increased capacity of torque transmission for the direct-coupling clutch.
Generally, the front cover is manufactured by means of press forming in order to achieve improved productivity and reduced manufacturing cost and also the front wall portion of the front cover disposed opposite to the clutch disk and the peripheral portion of the front cover for securely joining with the pump impeller shell are connected by a curved connecting portion of a considerably large radius of curvature in order to assure the sufficient strength of the front cover. Therefore, it is extremely difficult to provide a frictional material of an increased outside diameter without increasing the outside diameter of the front cover when the front cover is manufactured by means of press forming.